In the cultivating or harvesting of crops, such as sugar beets, a tractor is ordinarily employed to pull a farm implement such as a beet harvester along the crop rows. In beet harvesting, rather precise, continuous alignment of the harvester with the rows of beets is required. It is extremely difficult to so steer the tractor as to maintain this precise alignment, as continuous, careful attention must be given by the tractor operator to the position of the tractor and harvester with respect to the rows of beets. As modern harvesters move through the fields at several miles per hour, even a momentary misalignment of the harvester may cause many beets to be missed.
Numerous efforts have been made to provide apparatus for sensing misalignment of a farm implement with a crop row and for shifting the farm implement back into alignment. Representative of such devices are those described in U.S. Pat. Nos. 3,461,967; 3,326,319 and 3,183,976. Such devices include a pair of row-sensing shoes which operate a hydraulic system to shift the trailing farm implement from one side to another. Devices of this type, however, do not take into consideration variances in the size of the plants (such as sugar beets), often are slow acting, and may not be accurate in aligning the farm implement with the plants whose position is sensed.
Moreover, problems have also been encountered particularly with cultivating and beet harvesting equipment, in digging too deeply for the beets or in passing over and missing the beets entirely as the implement moves along a crop row. This in turn may be caused by rolling land contours, soft or muddy spots in the field in which the tractor and implement tires partially sink, etc. Various devices have been proposed for automatically maintaining the level of a farm implement such as a cultivator with respect to the ground, and among such devices may be listed that of my U.S. Pat. No. 3,844,357. The height-sensing devices, however, do not take into consideration side-to-side variances in the alignment of a harvester with a crop row, nor do such devices account for dips or soft spots or the like in the ground to either side of the crop row which may be encountered by the tractor or implement tires. That is, such devices ordinarily react only to the level of a single ground level-sensing shoe or foot.
As a result, farmers must exercise extreme care in maintaining the precise position of the tractor with respect to a crop row, and are often simply unable to insure that substantially all of the plants in the crop row will be properly cultivated or harvested or the like. Since modern agricultural methods stress speed of cultivation and harvesting, and make use of expensive and highly elaborate equipment, it is often not practical to return a harvesting device, for example, to harvest plants which were missed because the harvester had been misaligned with the crop row.
A device which would automatically center a farm implement with respect to a crop row and which would additionally and automatically maintain the proper height of the implement with respect to the ground level, is greatly to be desired.